Easyvibe LFO guidance

Mr Eastwood · July 13, 2019, 09:26:50 AM

Hi, i'm in the process of building my first pedal which is the Easyvibe on a breadboard; my idea is to build the circuit in stages so I can test each stage and after it's all working I could play around with the circuit a bit.

I have sketched out (see pic) of what I have built up so far but I can't seem to get my leds pulsating; so i have a couple of questions.

1. Are the opamps shown in my pic (a,b,c) all fed with a supply of +9 and 0v ?
2. if i wanted to build just the basic LFO part so I can check it working / oscillating correctly on my scope, then i'd only have to build the part outlined in red in the circuit?

Thanks in advance.

GibsonGM · July 13, 2019, 09:36:21 AM

Hi Eastwood, welcome.

1) Yes! You really have 9V, the bias voltage at the 10k resistor and 470u cap, and ground (0V). Opamp power pins are 9V and 0V.

2) Yes! But I'd also include the diode stuff below the opamps, and the depth opamp, drive pot. Everything down that part of the drawing. I have done just that, and it works. Then you will know it is actually driving the LEDs you're using. It is a good LFO for other projects, too.

duck_arse · July 13, 2019, 10:16:03 AM

also welcome. Eastwood is only one suburb away from here.

I agree with everything^* Sir Mike says, especially the part about adding pin-numbers to your circuits [helps us check your work], and when he says show us photos of your work, please, even if just the breadboard, and most especially of all when he says what are your voltage measures around the opamp?

* except I don't think you need the stuff below the red line.

ohh, and not VCO, LFO.

GibsonGM · July 13, 2019, 11:10:31 AM

Ok. I figured 'the stuff', the diodes, were to make the 4 LEDs operate properly. And of course 'depth' is depth. When I've used this, I've just kept it all as-is and used the LEDs in a project, but as the Duck says, not entirely necessary to do so...

Mr Eastwood · July 13, 2019, 12:55:22 PM

Thanks for all your really helpfully comments!

I changed the thread title from "VCO" to "LFO" (my bad!)

Perhaps I'm just missing a wire link or something - i'll take another look now.

Mr Eastwood · July 13, 2019, 02:32:25 PM

I feel so stupid! one of the leds in the power rail wasn't in the breadboard properly because i was trying to straddle too many holes without bending the legs properly; in my defence they were short legged salvaged leds, lol

As soon as that was fixed i saw a nice wave on my scope and the LFO leds are pulsating like a, well like a univibe

So, now all i need to do is build up the 4 stage. "phase shift" things ?

ElectricDruid · July 13, 2019, 07:19:58 PM

Quote from: Mr Eastwood on July 13, 2019, 02:32:25 PM
So, now all i need to do is build up the 4 stage. "phase shift" things ?

I love it when a plan comes together!

Mr Eastwood · July 14, 2019, 02:42:42 AM

I finished the final part of the build last night, so i'll come back to it with fresh eyes perhaps later today to see if I missed anything, then I can hook it up and test it, I will report back how that goes

GibsonGM · July 14, 2019, 09:09:55 AM

Awesome! Hope it works.

So, now all i need to do is build up the 4 stage. "phase shift" things ?

Yup...that's why I suggested leaving the LEDs and that lower stuff in place!

duck_arse · July 14, 2019, 10:05:03 AM

looks like it's "gold knobs" week!

nice scope.

Mr Eastwood · July 15, 2019, 07:51:15 AM

Yay - it works!

I just need to work on the bias / photocells and leds to get a bit more depth to it, I only used tape around the photo / leds so i'm prob loosing some depth there. I'm going to look forward to playing around with this circuit.

Mr Eastwood · July 21, 2019, 08:49:07 AM

hah - it turned out the lack of depth was because my wire jumper was in the chorus mode! lol

Mr Eastwood · July 31, 2019, 08:34:08 AM

ok. so I swapped out the red leds for super-bright white leds - which chews a bit more current but that's ok as the final build will be jack powered. and I like the sound, it's pretty nice and clean. I added a fet to drive the leds and then used my function generator to push through different waveforms with different offsets (bypassing the LFO); I liked the sawtooth best - i played with the waveform symmetry but found it was best in the middle. I was thinking of replacing the LFO with a microcontroller, but that will be for version 2 of my circuit; at the moment i've ordered jacks / case etc and i'm just designing the pcb for it.

Has anyone tried the easyvibe with a bulb? does that give it that "deep vibe" sound? I read a load of forum posts but I'm not sure if it was tried? I'd like to have a switch to toggle between "clean" vibe and "deep" vibe; any pointers? I really like the simplicity of the easyvibe circuit so i'd like to bend that into the "deep" vibe rather than have 2nd complete circuit on the same pcb. Does the bulb give a more linear resistance in the LDR, thus a deeper vibe?

Mr Eastwood · August 02, 2019, 05:57:31 PM

I just tried a couple of 6v wheat bulbs, works much better for me

GibsonGM · August 02, 2019, 09:39:27 PM

Quote from: Mr Eastwood on August 02, 2019, 05:57:31 PM
I just tried a couple of 6v wheat bulbs, works much better for me

Time for a sound clip, perhaps?

Rob Strand · August 03, 2019, 12:05:36 AM

Quotedoes that give it that "deep vibe" sound?

There's two variables to play with: the width of the LFO sweep and the offset (ie. shifting the waveform up and down).

You might be able to get the deeper sweep by putting a Schottky diode in series with the opto LEDs. You could try a silicon diode but it might be too much. On the real univibe the lamp drive adjusts both the offset and the sweep at the same time and that deep sweep was set-up using that single adjustment. JC Maillet's viva analog site is one of the few places I've actually seen that drawn up. He also adds an offset adjustment so the offset can be adjusted independently of the sweep width. The EasyVibe edges on the deep sweep by matching up the Diode + 2xLEDs on the bias circuit with the 2xLED on the LED drive circuit. Adding a Schottky will push the LEDs closer to cut-off.

For the lamps you will have to experiment with how many series diodes to add. The opamp in the EasyVibe is probably pushing it to drive lamps.

Mr Eastwood · August 04, 2019, 07:28:49 PM

This is my idea for my LFO stage, this little circuit I made uses a microcontroller and 12bit DAC, so potentially I can code it to spit out any custom waveform/s i need. I created a simple triangle waveform to start with. The reason why i've done it like this is I can tweak the offset based on a rate setting. well that's the plan anyway.

[edit: I also need to try some bigger light bulbs and see what they sound like. ]

ElectricDruid · August 05, 2019, 04:08:54 AM

Aah, the wonders of the uP-controlled LFO! Nice to see other people coming to the party!

T.

Mr Eastwood · June 16, 2020, 12:50:28 PM

Hi, I just wanted to share an update on my project; well I got back to this project a few weeks back and decided to put it into a PCB; i've made the first one up and I'm happy with the sound, although I need to re-spin the board as i made a couple of mistakes on it.

ok so here's a phone sound-clip of my "Junivibe" which is basically the Easyvibe but with bulbs and sry for the bad playing! lol

Eb7+9 · June 16, 2020, 09:38:50 PM

unusually good work Jules ...

from your clip I'm not hearing a "lacking" Vibe sound, which would indicate basic cell range adequacy
you obviously understand the role of OFFSET here, so try getting wider-range cells if you're looking for more phasing

tell us more about your LFO structure if you can ... (some of us are still stuck in the 60's)
I'm curious what a SPEED dependent offset would do for you on a PIC derived waveform ...

good chops btw

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Easyvibe LFO guidance